Main battle tanks, such as the U.S. Army's M1A1 Abrams Tank, are sometimes stored and thus have less cannon firing activity than tanks which are assigned to active military units. Even tanks in active units may not be fired for prolonged periods. The gun mount assembly, which absorbs the recoil energy of the cannon when it is fired, can be harmed by these lengthy periods of inactivity. The assembly functions similarly to a shock absorber on an automobile and contains hydraulic fluid which is used as the primary energy absorbing medium. The gun mount assembly has dynamic seals which contain the hydraulic fluid under pressure. These seals remain well lubricated on tank cannons which are continually fired. On cannons that are rarely fired, these seals can dry out, become brittle, and are subject to adhesion with mating metal surfaces. Under these conditions, seals can degrade and fail immediately when put back into service. Seal failure leads to an excessive leakage of hydraulic fluid from the gun mount assembly. A tank cannon with failed seals is unfit for service since an attempt to fire the cannon will result in catastrophic failure of the gun mount assembly. The failure will result from insufficient energy absorbtion by hydraulic fluid in the gun mount assembly.
There are now only two standard methods for exercising guns, i.e., causing them to imitate their recoil motion so as to wet the dynamic seals with hydraulic fluid. The first method involves a wrecker vehicle using its hoist to push against the end of the cannon barrel. The second method involves the use of a hand pump (such as the U.S. Army M3 hand pump) which fills the gun mount assembly with extra hydraulic fluid, thus pushing the cannon out of the battery and thereby lubricating the dynamic seals. These procedures have been in existence since the advent of the U.S. Army's M60 tanks in the 1950's.
Tanks in storage warehouses are parked very close together. The space between any two tanks is normally 12 to 18 inches. Typically there are 60 tanks in a building and the tanks are stored without fuel or batteries. To exercise the gun mount assemblies of these tanks using a wrecker, the tanks have fuel and batteries installed. The tanks must then be driven out of the building so that the wrecker has room to get in front of each tank and push the tank's gun barrel with the wrecker hoist. In addition to wasting fuel, the wrecker method is labor intensive and usually takes 6 personnel about a week to exercise all 60 tanks in the building. Additionally, the controls operating the hoist are unable to stop the hoist at exact locations, so that there is a possibility of pushing the gun barrel beyond design limits for recoil travel. Also, it is not always possible for the hoist to apply force at the end of the gun barrel exactly parallel to the gun barrel. This means that the hoist tends to lift or lower the barrel while pushing it, thus placing potentially harmful loads on the gun mount assembly and the gun elevation system.
To exercise the gun mount assemblies using the M3 hand pump, one must enter the vehicle to connect the hand pump directly to a fitting on the gun mount assembly. To do this, one must first remove a replenisher hose on the fitting that leads from a hydraulic fluid reservoir, thereby spilling fluid onto the floor of the tank. Also, opening the hydraulic system to air may cause fluid contamination and consequent corrosion of internal gun mount assembly components and shorter seal life. Furthermore, when using the U.S. Army's M3 hand pump to exercise the gun mount, one needs 400 to 500 strokes of the pump handle to provide sufficient force to push the cannon barrel back the required exercising distance of 6 to 8 inches. Since the gun mount system on which the M3 is used must be exercised 3 times, the number of M3 pump strokes needed to fully exercise the gun mount assembly is 1200 to 1500 strokes.